The present invention relates generally to electronic film developing and more particularly, to apparatus and methods for determining the optimum exposure of pixels in a time-scanned film image.
Chemical film development traditionally involves the chemical manipulation of an entire image which has been recorded on conventional film. Conventional film includes multiple layers of varying granularity distributions of silver halide crystals. Broadly stated, multiple film layers are used with color film to separately capture and reproduce color information. The crystal granularity distributions further provide for capturing image details under different lighting and/or desired film exposure conditions or xe2x80x9cspeedsxe2x80x9d. That is, larger or more xe2x80x9ccoarsely-grainedxe2x80x9d crystals require exposure to fewer photons of light during picture-taking to enable proper developing. Conversely, smaller or more xe2x80x9cfine-grainedxe2x80x9d crystals that together encompass an area equal to that of a single larger grain will require more light during picture-taking to enable proper developing of each grain. Modem color film typically uses three layers or xe2x80x9cemulsion coatingsxe2x80x9d for each color, each with a different granularity distribution, thereby enabling image detail to be recorded on the film at varying exposures for each color.
Unfortunately, while film can be viewed as recording all essential picture information, conventional chemical processing does not enable optimal reproduction of individual picture elements. More specifically, different picture elements such as highlights, midtones and shadows, while recorded on the same film layer, each require a different amount of development time to be optimally reproduced. Highlights, for example, might be optimally developed in one minute while midtones might require two minutes and shadows might require four minutes. However, chemical processing develops all picture elements at the same time. Thus, a compromise or approximation must be made as to an acceptable development time for accommodating all image elements.
Conventional techniques have been developed to improve the overall quality of a picture by taking into account varying developing time requirements. However, the resulting picture element handling capabilities are nevertheless subject to chemical processing limitations. For example, using monochrome film having multiple granularity distribution, and thus varying exposure-sensitivity layers, multiple exposures of a single still image can be recorded and later merged in a darkroom. However, such techniques still provide only gross adjustments to multiple picture element combinations, and require extensive effort and often specialized film and/or processing to do so.
Digital film processing (xe2x80x9cDFPxe2x80x9d) takes an entirely different approach. DFP provides for capturing raw image data directly from the film itself while it is being developed. Each channel (such as red, green, blue) of each element or pixel will typically be captured separately at multiple developing time increments or timed-scans. The pixel data of each timed-scan is then analyzed and/or manipulated to provide optimally an image that uses the appropriate exposure for each pixel.
FIG. 1 illustrates certain aspects of a DFP system taught in U.S. Pat. No. 5,519,510, and is taken from FIG. 9 of that patent. As shown, the DFP system provides scanning a system for scanning an image recorded on film 101 directly from film 101 while film 101 is being developed. At multiple times during development of film 101, infrared light sources 104 or light-source-array projects infrared light 11 and 12 at color film 101 and a portion of the image is captured (i.e. xe2x80x9ctimed-scannedxe2x80x9d). Scanning a three-layer film 101, for example, includes capturing reflected light 11 from portions (e.g. portion 11a) contained in the first or xe2x80x9cfrontxe2x80x9d film layer 111 and capturing reflected light 12 from portions (e.g. portion 12a) contained in a third or xe2x80x9cbackxe2x80x9d film layer 113. Portions (e.g. portion 11a) contained in the second (i.e. xe2x80x9cmiddlexe2x80x9d or xe2x80x9cthroughxe2x80x9d) layer are also captured by scanning transmitted light 11 passing through film 101, from which scanned front layer and back layer values for corresponding front layer and back layer portion scans are then subtracted. This process is repeated for each portion, thereby producing front-layer, middle-layer and back-layer portion information for each portion position at each timed-scan during development of film 101. Scanned portion information (or xe2x80x9cpixel informationxe2x80x9d) is then processed as described hereinafter with reference to FIGS. 2a-3.
As shown in FIG. 2a, during picture-taking with camera 210, a single picture 201 recorded onto film 101 or xe2x80x9cexposedxe2x80x9d film (FIG. 1) will typically include discernable picture elements such as highlights 211a, midtones 211b and shadows 211c. 
Turning to FIG. 2b, exposed film 101 is then subjected to DFP processing. First, the above-mentioned timed-scans are taken using scanning system. During processing of film 101, an early scan 202a (e.g. one minute) will best reveal pixels corresponding to highlights 211a, while midtones 211b and shadows 211c will be underdeveloped. A later scan (e.g. two minutes) will better reveal midtones 211b, while highlights 211a will become overdeveloped. Still later scans will better reveal shadows 211c at the expense of highlights 211a and midtones 211b. 
FIG. 3 illustrates that while several timed-scans are typically taken, not all of the scans obtained throughout film development are typically required. Rather, a sufficient number of scans are desirably taken such that the optimal exposure of selected picture elements in each film layer can be deduced by extrapolating from the limited number of scans actually taken. Individual scans can further be combined to reduce memory requirements. For example, scans 302 and 304 can be combined to produces scan 308.
FIG. 3 also illustrates how the DFP system further provides an image-based processing/stitching system for processing and merging of groups of picture elements in order to form a completed processed image. Creating a merged image will be generally referred to herein as xe2x80x9cstitchingxe2x80x9d regardless of the specific implementation utilized. As taught in the 510 patent, an approximation is preferably made as to the best exposure for different groups of picture elements utilized (i.e. in this case, highlight, midtone and shadow portions of the image stored on the film). Next, the different groups of picture elements can be combined by aligning, cutting and pasting them together 320 to yield the finished image 322.
Unfortunately, if many timed-scans are needed, memory requirements become exorbitant. Accordingly, when fewer timed-scans are used, or when the actual time-scan time varies from the desired time-scan time, estimates of timed-scans which estimates were not reliable, needed to be made in order for the groups of picture elements to appear as a single continuous picture. Thus, adjustment approximations according to available scanned data were required, often yielding less-than-ideal results and often requiring significant computation.
U.S. Patent Application Ser. No. 60,075,562, filed Feb. 23, 1998, entitled xe2x80x9cParametric Image Stitchingxe2x80x9d teaches an alternative method of stitching, and is hereby expressly incorporated by reference. In that application, the tedium of pasting groups of picture elements is replaced by forming a mathematical model representing the recorded image and then resolving the model as a completed image. Modeling, in this instance, generally includes the ability to process stitch picture elements (e.g. pixels) without reference to the overall picture formed on the film. As described, received timed-scan pixel data is tagged with the time of capture (i.e. a relative and/or absolute indicator of the time of each scan during the course of film processing). Then, for each pixel at each time, regression parameters are calculated and summed, the optimal density of each pixel position on the film is predicted, a gamma correction function is applied, and a brightness value for each pixel is determined.
More specifically, as shown in FIG. 4, different curves representing low, medium and high exposure timed-scans were obtained for each pixel based upon a xe2x80x9cbest fitxe2x80x9d of the received pixel data for each of the different timed-scans. Also, an optimum density curve is empirically derived, as shown by dotted line 404. According to this application, the actual best xe2x80x9cbrightnessxe2x80x9d for a pixel can be determined based upon the intersection of the optimum density curve with the best fit curve depending upon the characteristic of the pixel, i.e. whether it was a low, mid or high exposure pixel.
Unfortunately, this implementation not only requires substantial computation, but again ultimately results in a predicted approximation of the optimal exposure. Thus, the determined brightness value nevertheless might result in an inaccurate reproduction of the filmed subject. Accordingly, there remains a need for an DPF stitching method that provides a more accurate reproduction of a filmed subject. There is further a need for an DPF stitching method having reduced computational requirements.
It is an object of the present invention to provide a method of directly determining the exposure, or brightness, of a given pixel of data associated with a portion of a scanned image of a developing negative.
It is a further object of the present invention to directly determine exposure information associated with each layer of a multi-layer color film, for each pixel.
These and other advantages are provided for by the present invention through a digital processing system in which signals associated with a pixel are obtained at each of a plurality of different development times of the film being developed. A regression analysis that compares these different development times versus the natural log of time is made, to obtain a best fit line of this data, which line is then used to determine a xe2x80x9cbxe2x80x9d value. This xe2x80x9cbxe2x80x9d value or xe2x80x9cfitting constantxe2x80x9d preferably corresponds to the intersection of the y-intercept and the best fit line. It has been discovered that this xe2x80x9cbxe2x80x9d value is substantially directly proportional to the log exposure of the pixel. Accordingly, this xe2x80x9cbxe2x80x9d value can be directly used to determine the appropriate exposure of the pixel.